Spin drift question

[kwilliams]

Surely this has been addressed in the past, but a new concern of mine. What kind of drift in inches does the .40 and .45 veer off line of sight at 1000-1200 yds. with the usual 1-14 to 1-18 twist. Since I have never shot that distance on a dead calm day I am wondering what the sight correction would be for it. My basic zero is 600 yd at home on the rare calm day.
thanks
kw

[rdnck]

With a dead on zero at 100 yards, and assuming dead calm conditions--good luck with that--spin drift at 1000 yards will be in the neighborhood of 30 inches. So give yourself about three to three and a half minutes left windage to start provided your rifle has a right hand twist. Shoot straight, rdnck.

[45bpcr]

Best question I've seen asked here in a while.
I hope you get decent answers Rdnck.

[kwilliams]

Thank you for the reply. 30 inches is a number to remember and adjust accordingly.
best
kw

[bpcr shooter]

And Coriolis effect......

if you’re shooting West, your target’s gonna rotate up and towards you, which is gonna cause the bullets to hit lower and if you’re facing east, the target’s going to be dropping and slightly moving away, which is gonna cause the hits to be higher. For modern bullets this can be 7-10in at 1k, so with our super speedy bullets.....a tick more

[COBPTR]

15 to 20 inches from a 200yd zero.
You can sight your rifle in to hit 1.5-2" left at 200, or you can cant your sight 1.5 degrees to the left of plumb when your front sight level is center bubble. Then "theoretically" you could shoot from 200-1000 and be close to zeroed.
Best option is to have a MR/Silhouette rifle and a dedicated LR rifle. Twice the money but twice the fun!

Robert G.

[desert deuce]

It is not Friday, however, I feel compelled to engage in some confession. Some say it is good for the soul. Assuming the existence of one. So I will throw this out there for the Father Confessors in the peanut gallery.

I don't worry about such things with a 40-65 as I don't shoot beyond silhouette rams with one and that's good enough for target. I set it 0.0 at 200 yards for silhouette and midrange. It just hasn't occurred to me to try the .40 beyond 600 yards as I have 44-90's and 45-90's for that.

I do what Robert suggests with the 1.5 Degree cant, Plus, 2.0" left at 100 yards, for shooting 800 yards and beyond with the 45-90. No science involved just a habit developed over time foisted upon me initially by Dan T. Additionally, I have wind gauge front sights on my long range rifles because I have noticed a "relative" dead wind zero seems to vary depending on where on the planet I am shooting. Nobody suggested this, I just evolved into it and later found out at least one of the top long range shooters in the country does essentially the same thing. Why? He doesn't really know either other than it works for him.

What have I found? Elevation in particular is an elusive beast for long range. Can vary 5 minutes from one relay to another my rifle, my load. I suspect environmental conditions figure into that variable but can't quantify it logically, just have observed that something does it on occasion. I don't worry about it as the remedy is the elevation screw on the soule sight. Which takes us back to the lesson of the day, every day. BELIEVE THE TARGET.

[bruce m]

the nearest i can get is about 2 moa for a 45 cal bullet in an 18 twist.
3 moa for a 40 cal with a 13 twist.
bruce.

[bruce m]

just worked out the 45 cal on j b m ballistic calculations and it comes to 3.3 moa at 1000 yds with 18 twist.
if it is 6 moa to the edge of the target from the centre?, you are at a disadvantage on the first sighter if you make no allowance.
you are also going to have trouble if the wind goes across centre in a big way.
bruce.

[Distant Thunder]

Ok, so with a scope do I cant that 1 1/2 degrees to the left also or do I just turn the very expensive knob that came with the scope and write down the setting? Just wondering!

[BFD]

Ok, so with a scope do I cant that 1 1/2 degrees to the left also or do I just turn the very expensive knob that came with the scope and write down the setting? Just wondering!

1.5 degrees? That's 90 minutes. - you'll be shooting on Target 7...

[Distant Thunder]

So is that minutes or points? It's all so confusing! I think I'll just keep doing what I've been doing, it seems to work and I get to turn the knobs and that makes me feel like I'm in control.

[sandhillcowboy1]

Shooting at long range and canting your sight to the left for a right twist barrel eliminates a variable, the least amount of variables involved in shooting BPCR is always a good thing. I use a shim under the right side of my MVA mounting bracket. Then take it out to the range and try it on a windless day (impossible almost here) from short to long distance. Adjust thickness of shim as needed. The ODG's in the 1880's had the Buffington sights on trapdoors canted to the left for long range shooting, maybe they were smarter than we are today:)

Rick

[Tasmanian Rebel]

Question for you .22 shooters out there. Have you seen drift with your .22's at the 200 yd line? I've been tinkering with mine and have so far seen little if any although I would expect to see some I would think.
Keith Lay

[Kurt]

LOL, I have a natural cant. I hope it's in the right direction. LOL